The present invention involves the field of surgery, and particularly surgical instruments and methods of using the same.
A variety of physical conditions involve two tissue surfaces that, for treatment of the condition, need to be distracted from one another and then supported away from one another. Such distraction may be to gain exposure to select tissue structures, to apply a therapeutic pressure to select tissues, to return tissue structures to their anatomic position and form, or in some cases to deliver a drug or growth factor to alter, influence or deter further growth of select tissues. Depending on the condition being treated, the tissue surfaces may be opposed or contiguous and may be bone, skin, soft tissue, or a combination thereof. An optimal treatment method includes distracting and supporting the tissue surfaces simultaneously.
A minimally invasive distraction and support device would have significant application in orthopaedic surgical procedures, including acute and elective procedures to treat bone fractures and degenerative changes of the skeletal system and including vertebral compression fractures, interbody fusion, vertebral disc augmentation or replacement, and other compression fractures including, but not limited to tibial plateau compression fractures, calcaneous compression fractures, distal tibia fractures, distal radius (wrist) fractures, crushed or fractured orbit and orthopaedic oncology. Further, a minimally invasive distraction and support device would have application in non-orthopaedic surgical procedures in plastic surgery (for example facial reconstruction), gastrointestinal surgery and urological surgery (for example the treatment of incontinence).
Vertebral Compression Fractures
A vertebral compression fracture is a crushing injury to one or more vertebrae. Vertebral fractures are generally associated with osteoporosis (the xe2x80x9cbrittle bonexe2x80x9d disease), metastasis, and/or trauma. Osteoporosis reduces bone density, thereby weakening bones and predisposing them to fracture.
The osteoporosis-weakened bones can collapse during normal activity. In severe cases of osteoporosis, actions as simple as bending forward can be enough to cause a vertebral compression fracture. Vertebral compression fractures are the most common type of osteoporotic fractures according to the National Institute of Health. The mechanism of these fractures is one of flexion with axial compression where even minor events cause damage to the weak bone. While the fractures may heal without intervention, the crushed bone may fail to heal adequately. Moreover, if the bones are allowed to heal on their own, the spine will be deformed to the extent the vertebrae were compressed by the fracture. Spinal deformity may lead to breathing and gastrointestinal complications, and adverse loading of adjacent vertebrae.
Vertebral fractures happen most frequently at the thoracolumbar junction, with a relatively normal distribution of fractures around this point. Vertebral fractures can permanently alter the shape and strength of the spine. Commonly, they cause loss of height and a humped back. This disorder (called kyphosis or xe2x80x9cdowager""s humpxe2x80x9d) is an exaggeration of the spinal curve that causes the shoulders to slump forward and the top of the back to look enlarged and humped. In severe cases, the body""s center of mass is moved further away from the spine resulting in increased bending moment on the spine and increased loading of individual vertebrae.
Another contributing factor to vertebral fractures is metastatic disease. When cancer cells spread to the spine, the cancer may cause destruction of part of the vertebra, weakening and predisposing the bone to fracture.
Osteoporosis and metastatic disease are common root causes leading to vertebral fractures, but trauma to healthy vertebrae also causes minor to severe fractures. Such trauma may result from a fall, a forceful jump, a car accident, or any event that stresses the spine past its breaking point. The resulting fractures typically are compression fractures or burst fractures.
Vertebral fractures can occur without pain. However, they often cause a severe xe2x80x9cband-likexe2x80x9d pain that radiates from the spine around both sides of the body. It is commonly believed that the source of acute pain in compression fractures is the result of instability at the fracture site, allowing motion that irritates nerves in and around the vertebrae.
Until recently, treatment of vertebral compression fractures has consisted of conservative measures including rest, analgesics, dietary, and medical regimens to restore bone density or prevent further bone loss, avoidance of injury, and bracing. Unfortunately, the typical patient is an elderly person who generally does not tolerate extended bed rest well. As a result, minimally invasive surgical methods for treating vertebral compression fractures have recently been introduced and are gaining popularity.
One technique used to treat vertebral compression fractures is injection of bone filler into the fractured vertebral body. This procedure is commonly referred to as percutaneous vertebroplasty. Vertebroplasty involves injecting bone filler (for example, bone cement) into the collapsed vertebra to stabilize and strengthen the crushed bone.
In vertebroplasty, physicians typically use one of two surgical approaches to access thoracic and lumbar vertebral bodies: transpedicular or extrapedicular. The transpedicular approach involves the placement of a needle or wire through the pedicle into the vertebral body, and the physician may choose to use either a unilateral access or bilateral transpedicular approach. The second approach, the extrapedicular technique, involves an entry point through the posterolateral corner of the vertebral body. The needle entry point is typically 8 cm to 12 cm lateral of the mid-sagittal plane, with the skin incision typically closer to 8 cm in the proximal spine and generally closer to 12 cm in the distal spine. In general, one cannula is placed to fill the vertebral body with the extra-pedicular approach.
Regardless of the surgical approach, the physician generally places a small diameter guide wire or needle along the path intended for the bone filler delivery needle. The guide wire is advanced into the vertebral body under fluoroscopic guidance to the delivery point within the vertebrae. The access channel into the vertebra may be enlarged to accommodate the delivery tube. In some cases, the delivery tube is placed directly and forms its own opening. In other cases, an access cannula is placed over the guide wire and advanced into the vertebral body. After placement, the cannula is replaced with the delivery tube, which is passed over the guide pin. In both cases, a hollow needle or similar tube is placed into the vertebral body and used to deliver the bone filler into the vertebra.
In this procedure, lower viscosities and higher pressures tend to disperse the bone filler throughout the vertebral body. However, such conditions dramatically increase the risk of bone filler extravasation from the vertebral body. The transpedicular approach requires use of a relatively small needle (generally 11 gauge or smaller). In contrast, the extrapedicular approach provides sufficient room to accommodate a larger needle (up to 6 mm internal diameter in the lumbar region and lower thoracic regions). In general, the small diameter needle required for a transpedicular approach necessitates injecting the bone filler in a more liquid (less viscous) state. Further, the pressure required to flow bone filler through a small gauge needle is relatively high. The difficulty of controlling or stopping bone filler flow into injury sensitive areas increases as the required pressure increases. The larger needle used in the extrapedicular approach allows injection of bone filler in a thicker, more controllable viscous state. Therefore, many physicians now advocate the extrapedicular approach so that the bone filler may be delivered through a larger cannula under lower pressure.
Caution must be taken to prevent extravasation, with the greatest attention given to preventing posterior extravasation because it may cause spinal cord trauma. Physicians typically use fluoroscopic imaging to monitor bone filler propagation and to avoid flow into areas of critical concern. If a foraminal leak results, the patient may require surgical decompression and/or suffer paralysis.
Kyphoplasty is a modified vertebral fracture treatment that uses one or two balloons, similar to angioplasty balloons, to attempt to reduce the fracture and restore vertebral height prior to injecting the bone filler. Two balloons are typically introduced into the vertebra via bilateral transpedicular cannulae. The balloons are inflated to reduce the fracture. After the balloon(s) is deflated and removed, leaving a relatively empty cavity, bone cement is injected into the vertebra. In theory, inflation of the balloons restores vertebral height. However, it is difficult to consistently attain meaningful height restoration. It appears the inconsistent results are due, in part, to the manner in which the balloon expands in a compressible media and the structural orientation of the trabecular bone within the vertebra.
Tibial Plateau Compression Fractures
A tibial plateau fracture is a crushing injury to one or both of the tibial condyles resulting in a depression in the articular surface of the condyle. In conjunction with the compression fracture, there may be a splitting fracture of the tibial plateau. Appropriate treatment for compression fractures depends on the severity of the fracture. Minimally displaced compression fractures may be stabilized in a cast or brace without surgical intervention. More severely displaced compression with or without displacement fractures are treated via open reduction and internal fixation.
Typically, the underside of the compression fracture is accessed either through a window cut (a relatively small resection) into the side of the tibia or by opening or displacing a splitting fracture. A bone elevator is then used to reduce the fracture and align the articular surface of the tibial condyle. A fluoroscope or arthroscope may be used to visualize and confirm the reduction. Bone filler is placed into the cavity under the reduced compression fracture to maintain the reduction. If a window was cut into the side of the tibia, the window is packed with graft material and may be secured with a bone plate. If a splitting fracture was opened to gain access, then the fracture is reduced and may be stabilized with bone screws, bone plate and screws, or a buttress plate and screws. (Both of these methods are very invasive and require extensive rehabilitation.)
Spinal Interbody Fusion
Spinal fusion is most frequently indicated to treat chronic back pain associated with instability or degenerative disc disease that has not responded to less invasive treatments. Fusion is also prescribed to treat trauma and congenital deformities. Spinal fusion involves removal of the spinal disc and fusing or joining the two adjacent vertebrae. The primary objective for patients suffering from instability is to diminish the patient""s pain by reducing spinal motion.
Spinal fusions are generally categorized into two large groups: instrumented and non-instrumented. In non-instrumented procedures, the physician removes tissue from the unstable disc space and fills it with some form of bone graft that facilitates the fusion of the two adjacent vertebral bodies. Instrumented procedures are similar to non-instrumented procedures, except that implants (generally metallic) are also applied to further stabilize the vertebrae and improve the likelihood of fusion.
Conventional instrumented procedures generally utilize plates, rods, hooks, and/or pedicle screws through various surgical approaches. These conventional implants are secured to the vertebral bodies that are being fused. Interbody fusion devices were introduced in the 1990""s as a less invasive surgical alternative, although interbody devices are increasingly being used in conjunction with pedicle screws. Interbody devices are implanted into the disc space to restore the normal disc spacing, utilizing tension in the annulus to stabilize the fusion unit. Interbody fusion provides a large area of the vertebral end plate for establishing bony fusion, a viable blood supply from the decorticated end plates, and dynamic compressive loading of the graft site. The interbody devices are generally filled with a bone filler to facilitate fusion. Interbody devices can be categorized in three primary groups: spinal fusion cages, which are available in a variety of shapes including rectangular, round-faced, and lordotic; allograft bone dowels and wedges (which are also available in various shapes); and titanium mesh (although titanium mesh is not itself a structural spacer).
Interbody fusion is typically completed through a posterior, an anterior, or a lateral intertransverse approach. Each of these techniques has limitations. Lumbar interbody fusion presents a challenging surgical procedure and relatively high pseudoarthrosis rates. As a result, this approach is increasingly combined with additional internal fixation devices such as pedicle screw fixation.
In all interbody surgical approaches, a relatively large opening is made in the annulus. The nuclear material is removed and the end plates are decorticated to facilitate bony fusion. Overall, the use of interbody devices has resulted in mixed clinical outcomes. Placement of a fixed height device presents challenges in proper tensioning of the annulus. For these and other reasons, there is concern over long-term stability of interbody devices and fusion mass.
The invention provides a combination of a temporary or long term implantable device and instrumentation to place the device, in which tissue surfaces are distracted along an axis to enable access to the space between the tissues. Generally, the invention provides wafers for stacking upon one another to provide an axially extending column to distract and support tissue surfaces. While a primary use of the invention is to reduce and stabilize vertebral compression fractures, the invention may be used in any situation where it is desirable to distract two tissue surfaces. The tissue may be bone, skin, soft tissue, or combinations thereof. Further, the surfaces may be opposed surfaces of contiguous elements or surfaces of opposed elements. Thus, the invention may be used to treat vertebral compression fractures, for replacement of vertebral discs, as an interbody fusion device, wedge opening high tibial osteotomy, tibial tuberosity elevation, as well as for treating other compression fractures including, but not limited to tibia plateau fractures, calcaneous, distal tibial fractures, or distal radius (wrist) fractures. The invention may also be used for restoring the floor of the orbit, for elevating soft tissue in cosmetic applications, or in incontinence applications as a urethral restrictor. Alternately, the invention may be used in similar veterinary applications.
The Distraction Device
The terms xe2x80x9cverticalxe2x80x9d, xe2x80x9cupxe2x80x9d, etc., are occasionally used herein for ease of understanding, and these terms should be taken in reference to the vertebrae of a standing patient. Thus, xe2x80x9cverticalxe2x80x9d refers generally to the axis of the spine. We may also utilize mutually perpendicular xe2x80x9cXxe2x80x9d, xe2x80x9cYxe2x80x9d and xe2x80x9cZxe2x80x9d axes to describe configurations and movement, with the Z-axis being the axis of the column of wafers, that is, the direction in which this column grows as wafers are added sequentially to it. The X-axis refers to the axis extending generally in the direction of movement of each wafer as it is advanced to a position beneath a preceding wafer, and the Y-axis is perpendicular to both the X- and Z-axes. The wafers are sometimes described with reference to permitted degrees of freedom or restraint when they are placed in a column. It should be understood that these permitted degrees of freedom or restraint refer to the permitted or restrained movement of one wafer with respect to an adjacent wafer along one or more of the three axes, and the permitted or restrained rotation between adjacent wafers about one or more of these axes.
The distraction device includes a plurality of stackable wafers designed for insertion between tissue surfaces to form a column. The wafer column is assembled in vivo to provide a distraction force as well as support and stabilization of the distracted tissue. Preferably, the wafers place distraction force in one direction only and thus provide directional distraction. The distraction device may be permanently implanted, in which case the wafer column may be used alone or in conjunction with a bone filler material. Alternately, the distraction device may be used temporarily to manipulate tissues and then removed.
In use, the wafers are preferably stacked between two tissue surfaces as they are implanted, thereby distracting and supporting the tissue surfaces simultaneously. In the vertebral compression fracture application, it is preferable to distract along the Z-axis (along the axis of the spine) to restore vertebral height. However, in other applications, it may be preferable to provide distraction in a different direction. The features of a wafer and a column of wafers will be described relative to position and direction. The top of a wafer or the top of the column is defined as the face of the wafer or column in the direction of distraction. The bottom of a wafer or the bottom of the column is defined as the face opposite the top face. In similar fashion, above and below a wafer or column implies along the top and bottom of the wafer or column, respectively. Each wafer has a leading edge that enters the forming column first and a trailing edge opposite the leading edge. The sides of the wafer are adjacent the leading and trailing edges and the top and bottom faces of the wafer. In general, the sides are longer than the leading and trailing edges, however the sides may be shorter than the leading and trailing edges. The axis of the column is defined as a line parallel to the direction of distraction.
During implantation, the wafers are stacked to form a column to simultaneously distract and support the two tissue surfaces. The invention provides that trailing wafers can be positioned above or below the leading wafers to form a column. In one embodiment, the wafers are designed to be beveled at both their leading and trailing edges so that when lined up end-to-end, force on the trailing edge of the trailing wafer causes its leading edge to slide below the trailing edge of the leading wafer, thereby lifting up the leading wafer. Likewise, the bevel of the leading and trailing edges may be reversed enabling insertion of a trailing wafer above a leading wafer. Alternately, the leading and trailing edges may be chevron shaped or curved when viewed from the side, enabling insertion of trailing wafers between any two leading wafers or on the top or bottom of the column. In another embodiment, the wafers may be configured with blunt edges wherein the wafers are stacked with the insertion instrument. In all embodiments, by repeating the process with consecutive wafers, the column height increases to restore vertebral height.
The specific configuration of each wafer may be altered to better suit the application for which the wafer will be used. For instance, the thickness of the wafer and the angle of the bevel may be varied to provide a mechanical advantage and insertion force within acceptable ranges for a given application. A more acute bevel angle will provide greater vertical force for a given insertion force. In addition, wafer thickness may be varied to increase or decrease resolution available to the physician in performing a given surgical procedure. A thinner wafer will provide greater displacement resolution and incremental force generation to the physician in performing the procedure. A variation of wafer thicknesses may be used in combination to form a column and multiple wafers may be inserted into the column simultaneously. The top and bottom faces of a wafer may be parallel or oblique to enable building a column that is straight or curved, respectively. Parallel or oblique-faced wafers may be used independently or in combination to build a column that has straight and/or curved sections.
In order to place the wafers between the tissue surfaces, a wafer inserter is positioned within the surgical site with access at its distal tip to the tissue surfaces to be distracted and supported. A wafer is placed on the track and a plunger is used to advance the wafer to the distal end of the track. This is repeated with consecutive wafers until a column of sufficient height is created per physician discretion. After the wafer(s) have been inserted, the insertion device is removed. The distal end of the insertion device may be manufactured from the same material as the wafers and/or be detachable. In this embodiment, the distal end of the insertion instrument would be detached after placing the wafer column, and the instrument removed.
Optionally, bone filler may be injected into the vertebra to further stabilize the distracted tissues. The first wafer inserted may be longer and/or wider than subsequent wafers. The size differential may facilitate bone filler flow around the wafers. In addition, the wafers can be designed with various tunnels, grooves, and/or holes to improve wafer encapsulation, bonding between the wafers and any injected bone filler, and to provide a pathway for bone filler to penetrate the wafer column.